Saturated heterocycles are significant structural components of a wide range of drugs. Drug action depends strongly on the conformational properties of the substrate, both in the free state and in the receptor-bound state. Two new, potentially useful families of drugs are the thiosugars, which already include an antifertility agent, and the homopiperazines, which include an antihypertensive and a coronary vasodilator. We will carry out the first comprehensive conformational studies of these systems, comparing them to the older families of pharmaceutically important saturated heterocycles, such as the natural sugars, the piperidines, and the piperazines. In addition, we will use piperidines and 1,3,5-triazanes to examine conformational changes, both static and dynamic, that occur as the small molecule is complexed with increasingly larger materials. These studies will shed new light on the role of conformation in drug action.